1. Field of the Invention
The present invention relates to semiconductor device packaging, and, more particularly, to a method or process for producing the ceramic substrates which serve as modules or carriers for integrated circuit devices. The surfaces of such substrates are capable of accepting thin layer conductive patterns so as to enable the connection to external inputs and outputs, as well as to internal layers, of densely organized integrated circuit chips.
2. Background Art
As integrated circuit technology has developed over the past several decades, certain materials have been preferred in the production of substrates for mounting or carrying the semiconductor chips in which complex, densely packed circuitry is embedded. In particular, because of their exceptional insulating properties, ceramics and glass ceramics have become the most preferred materials. However, in order to serve the purposes described, the substrates constituted of these materials are required to have a high degree of flatness; and also to possess a high quality surface, that is to say, the roughness of the surface must be in the range of 2,000 to 5,000 angstroms such that the required thin film conductors can be readily accommodated.
In order to provide background for the subject matter of the present invention, reference may be made to U.S. Pat. No. 4,159,295. That patent itself provides further background material, particularly with respect to a description of a number of techniques that have been adopted for producing ceramic substrates for use with thin film electronic circuits. The above noted patent also describes its invention as one involving a process for producing ceramic substrates according to which a substantially homogeneous extrudable ceramic mass, comprising a number of constituents in prescribed ranges, is vacuum extruded so as to achieve an endless relatively flat strip which is dried to a green state and, if the strip is to be used for thin layer circuits, is subjected to a plane parallel pressure of about 9,000 to 12,000 N/Cm.sup.2, and then is fired or sintered into rigid ceramic substrates.
It has been discovered by the present inventors that significant improvement can be effected in the generalized context of ceramic substrate fabrication by lapping the ceramic substrates prior to the conventional sintering step, whereby a smoother surface is realized for said substrates than is normally obtainable at the completion of the sintering operation. By generalized context is meant a process of producing ceramic substrates regardless of whether extrusion, foil casting or other techniques are employed, or whether single or multiple layers of ceramic are involved in their fabrication.
It is therefore a primary object of the present invention to provide an improved process for achieving ceramic substrates for integrated circuit packaging.
A further object is to reduce significantly the time taken for the processing of such substrates by eliminating or minimizing the conventional post-sintering lapping and grinding procedures.
Yet another object is to perform a lapping operation on the substrates at a stage in the process, that is, in the green state-before sintering-where warp and camber have been caused by the stresses introduced by the prior pressing or lamination stage.